A promising technique for fabricating objects of ultrapure materials involves the use of acoustic energy to hold an object away from the walls of a chamber while the object is heated to a molten state, to avoid contamination of the object by the walls of the chamber. The process appears especially promising for fabrication in microgravity environments where only small levitation forces are required. One type of system includes a metal horn having a rearward portion coupled to a piezoelectric transducer that generates the acoustic energy, and a forward portion coupled to gas in the heated chamber. The horn efficiently couples the acoustic energy, and helps isolate the transducer from the hot chamber. However, where very high temperatures such as over 2000.degree. C. are present in the chamber, there may be conductance of considerable heat through the horn and excessive heating of the transducer. A horn which minimized heat transmission while efficiently coupling acoustic energy from a transducer to the fluid in a chamber, would be of considerable value.